The Design,synthesis And Antifungal Activity Of Hymexazol Glycosides Based On A Biomimetic Synthesis Strategy

Plant fungal diseases have always threatened food security and national security seriously.To solve this problem,a large number of chemical pesticides are applied into the fields.With the deepening of scientific research,many hidden dangers have gradually emerged.First of all,it can aggravate the evolution of pathogenic fungi,make them resistant to drugs,and lead to the destruction of ecosystems.Moreover,it can enter the human body through the food web and lead many human diseases by the cumulative effects,because it is difficult to degrade.In recent years,a new concept of biological pesticides has been proposed,which has the characteristics of green,environmental protection,and high-efficiency targeting.Chitin resource is a renewable marine biological resource which has biocompatibility,broad-spectrum antibacterial activity,plant growth regulation.It is considered to be the most ideal raw material for biological pesticides.Although the agricultural activity of the chitin resources has not reached the commercial level,they have the potential to be improved.The chitin resources can play a synergistic effect by bonding multiple active molecules to obtain highly active chitin resource derivatives.Based on this concept,this research adopted a biomimetic synthesis strategy which a library of hymexazol glycosides were designed,referring to the plant metabolites of hymexazol.Due to the advantages of low price and easy availability of chitin resources,we used common glucosamine and acetylglucosamine as raw materials to carry out glycosylation reaction with hymexazol and various kinds of hymexazol intermediates.Then,four types of 36 hymexazol glycosides were synthesized.After verifying their chemical structures,the antifungal activity against six phytopathogenic fungi were also tested.Subsequently,the one which have the most antifungal activity in vitro was used as the object to measure the antifungal activity in vivo and explore its antifungal mechanism through direct and indirect methods.Lastly,the structure-activity analysis of the hymexazol glycosides was carried out with quantum chemistry theory and Gaussian software package.On this basis,the direction of structural optimization of the hymexazol glycosides was screened out.The specific research results are as follows:1)When halogenated sugars were used as sugar donors,hymexazol O-glycosides and N-glycosides were successfully synthesized by controlling the glycosylation conditions.Therefore,12 kinds of hymexazol glycosides were prepared.The antifungal activity in vitro proved that the antifungal activity of the N-glycosides is lower than that of the O-glycosides.And when the sugar unit is acetylglucosamine,the glycoside 18has the highest antifungal activity.The EC₅₀ and EC₉₀ of Alternaria alternata and Sclerotinia sclerotiorum were 1.58μg/m L,34.84μg/m L and 64.04μg/m L,255.70μg/m L,which were far better than the plant metabolites of hymexazol,and weaker than the positive control hymexazol.However,glycoside 18 can protect tobacco seedlings from Alternaria alternata at 100μg/m L,and the protection rate is as high as 100%,which is higher than the control effect of hymexazol.2)Ten N-linked hymexazol glucosamine conjugates were synthesized by glucosamine and brominated alkanes intermediates of the ketone-like structure of hymexazol.Ten O-linked hymexazol N-acetyl-glucosamine conjugates were synthesized by N-acetyl-glucosamine and alcohol intermediates of the hymexazol alcohol structure.Fore S-linked hymexazol N-acetyl-glucosamine conjugates were synthesized by N-acetyl-glucosamine and olefin intermediates of the hymexazol alcohol structure with photocatalyzed thio-ene click reaction.The antifungal activity in vitro of the above hymexazol glycoconjugates was tested.The introduction of a carbon chain between the active group and the sugar ring of hymexazol glycoside would severely reduce its antifungal activity.In addition,S-linked hymexazol glycosides formed by the introduction of sulfur atoms can enhance its antifungal activity.3)The cell wall morphology of Alternaria alternata affected by glycoside 18 was observed by SEM and TEM.And then the enzyme activity experiment verified that it can induce the chitinase activity of Alternaria alternata.Therefore,it is speculated that the induced chitinase activity may be one of antifungal mechanism of glycoside 18.In addition,through plant pot experiments,it is found that glycoside 18 can promote plant growth and significantly enhance the root activity of tobacco seedling.4)The molecular structures of hymexazol glycosides（4,7,11,16,17,18）were built and optimized by Gaussian software.By analyzing their MEP,HOMO and LUMO,it is found that the electron-rich region on the sugar ring of the glycoside 18 is more concentrated and the frontier orbital electrons are more active,which helps it can bind to the target more closely,so it has a higher antifungal activity.Based on these conclusions,it can directly and clearly point out the structural optimization of the hymexazol glycosides.In this thesis,36 kinds of hymexazol glycosides were first synthesized based on a biomimetic synthesis strategy.A hymexazol glycoside which have excellent antifungal activity was screened.The hymexazol glycoside was not only harmless to plants,but also has a strong effect of promoting plant growth.So,it has the potential to develop into a new type of green chemical pesticide against fungi.This paper also innovatively carried out the structure-activity relationship of the hymexazol glycosides based on the strategy of combining quantum chemistry theory and Gaussian software.The structural optimization of the hymexazol glycoside was pointed out on the basis of theoretical analysis.